Soybean protein and amino acid contents are important for soybean quality assessment. Soybeans grown in Western Canada, including Manitoba, have demonstrated lower crude protein values when compared to those grown in Eastern Canada, and the southern US, limiting opportunities for future development of the soy processing sector.

However, the focus on crude protein alone does not adequately capture the true feeding value of the soybeans, and focus should be placed on assessing the amino acid score (or Critical Amino Acid Value) of the Manitoba-grown soybeans in order to better position their nutritional value.  The current project was designed to evaluate the effects of genotype, environment and genotype × environment interactions on soybean protein and amino acid concentrations, using soybeans grown in Manitoba. This project focused on the usage of a non-destructive, simple and fast method for assessing protein and amino acid contents, namely near-infrared (NIR) spectroscopy. The predictive ability of the NIR calibration model and factors that influence the performance of NIR system were estimated. The effects of genotype, environment and genotype × environment interactions on soybean protein and amino acid contents were significant (P < 0.05). Among those factors, genotype dominated the main part of variation for all traits. Protein and amino acids responded differently to various environments, but the favorable planting environments for soybean protein and amino acids accumulation were still unclear. Statistical analysis identified varietals where protein and amino acid contents persisted across growing environments and cropping years. In agreement with observations made in other jurisdictions, the Critical Amino Acid Value (CAAV), the sum of 5 key amino acids for livestock nutrition, demonstrated a negative correlation with total protein.  The latter provides evidence that the nutritional value of soybeans may not be best represented by crude protein levels. The availability of NIR methods to assess the CAAV of whole soybeans positions a new tool for the industry to evaluate the feeding quality of Manitoba-grown soybeans, and assist the soy sector in selecting soybean varieties best suited for Manitoba growing conditions.